Pipe and other tubulars have been lined with tubular polymeric liners, e.g., polyethylene, nylon 11, etc., for many years. These systems have been used principally in offshore and onshore pipelines, and in downhole production tubulars. Generally, the liner resides in close-tolerance with the host pipe along its length, forming a stable composite system. See FIG. 1, which is a cutaway end view of a lined tubular.
Several installation techniques are known to the art. However, they have all retied upon one of two methods to insert the liner into the host tubular; either pulling or pushing from one end or the other. Typically, to pull liners in, a cable is used, or if in the vertical direction, weights in conjunction with gravity have been employed to the same effect. In pushing methods, usually a four-step cycle is used upon the liner, consisting of the steps of clamp-push-release-reposition.
Under the current art, the maximum length of an individual installation segment has been limited by the mechanical properties of the liner in concert with the friction drag accumulated during the insertion process.
For example, for polyethylene liners installed in diameter-reduced fashion, e.g., the known Titeliner(trademark) and Swageliner(trademark) systems and the like, installation lengths tend to average 2500 feet, and the maximum permissible length is approximately 5000 feet. Tensile loads, borne totally by the liner, continually climb throughout the insertion process, in proportion to distance pulled, with all the force being directed through the leading end of the liner. As a result, when longer lengths are attempted, the liner simply pulls apart.
In pushing methods, the practical lengths tend to be even shorter. The relatively flexible liners quickly assume an xe2x80x98S-curvexe2x80x99 within the host due to the pushing. The resultant friction against the host wall is thus amplified, and the process simply stalls.
Generally, in either case, bends in the host pipe substantially diminish achievable insertion length. Drag between the liner and the host pipe increases dramatically due to bends that the liner passes. The increase in lateral pressure due to a bend increases the total friction between the two elements. Lining of reeled pipe is virtually impossible, since all segments that are to be lined must be relatively straight for best effect.
The invention relates to a method of injecting liners into host tubulars. Fluid is pumped into the host pipe concurrent with introduction of the liner. The momentum and drag imparted by the fluid to the liner induces axial motion of the liner for insertion into the tubular. Also, the pressure of the fluid in the host maintains the liner in a reduced cross-section throughout the insertion process, minimizing drag.
The invention extends the maximum installation length. It facilitates the ability to insert a liner over long distances, into those lines where sectioning into short distances is impractical, or impossible; e.g., water crossings and restricted rights-of-way. It can also be used to install liner into reeled pipe as well as straight pipe. These benefits translate directly to lower project costs. Fewer insertion operations are necessary for any in-situ rehabilitation project where the line is multiply sectioned, resulting in reduced time, hardware and overall cost. The invention also permits lining of new host tubulars at a plant-site for improved logistics and quality control. A final benefit of the method is that less longitudinal stress is imparted on the liner, minimizing failure potential and thus enabling longer service life.
The method is equally suitable to both pipeline, i.e., essentially horizontal, and downhole, i.e., essentially vertical, applications.
Other features and advantages of the invention will become apparent from the following detailed description, in conjunction with the drawings.